update python version constraint to install async-timeout.

async-timeout library has effectively been upstreamed into Python 3.11+.
installing it for python >= 3.11 should not be necessary.

this will enable packaging valkey-py for fedora 39, which
comes with python 3.12 and does not conatin async-timeout 4.0.3 package.

see the deprecation notice:
https://github.com/aio-libs/async-timeout?tab=readme-ov-file#deprecated

Signed-off-by: Ali Gholami <ali.gholami@aiven.io>

Author: ali-gholami-aiven

requirements.txt

@@ -1 +1 @@
-async-timeout>=4.0.3
+async-timeout>=4.0.3; python_version<"3.11"

setup.py

@@ -36,7 +36,7 @@
     author_email="valkey-py@lists.valkey.io",
     python_requires=">=3.8",
     install_requires=[
-        'async-timeout>=4.0.3; python_version<="3.12"',
+        'async-timeout>=4.0.3; python_version<"3.11"',
     ],
     classifiers=[
         "Development Status :: 5 - Production/Stable",